1. Field of the Invention
The present invention relates to a video transmission system for sending a plurality of channels of digital video signals to a receiving apparatus such as a TV receiving set.
2. Description of Background Art
In recent years, along with the widespread use of DVDs and the start of digital TV broadcasting, equipment handling a digital video signal has become prevalent.
As an interface standard for connecting a sending apparatus (such as a DVD recorder/player and a digital AV tuner) that sends a video signal to a receiving apparatus (such as a digital TV) that receives the video signal, high definition multimedia interface (HDMI) is available. The HDMI standard, which stipulates interface specifications for transmitting a baseband digital video signal to a receiving apparatus, assumes its incorporation into consumer equipment with its compatibility with digital visual interface (DVI) widely adopted in personal computers being kept. One HDMI cable connecting a sending apparatus to a receiving apparatus permits transmission of baseband (uncompressed) video data and audio data.
Many of recent display apparatuses such as digital TVs are provided with a function such as the picture-in-picture function to permit simultaneous display of two or more screens, and the use range thereof is wide. The HDMI standard however basically allows transmission of only one channel of video data. If simultaneous transmission of two channels of video data is desired, two signal processing routes must be provided using two HDMI cables. In this case, in which two pairs of HDMI cables and HDMI connectors must be prepared, a system with very high cost will result.
The HDMI standard actually supports a method for achieving 2-channel simultaneous transmission using one cable. For this achievement, however, a type B HDMI connector is required, which has a sufficient number of terminals to transmit two channels of transmission minimized differential signaling (TMDS) differential signals.
The HDMI connectors and HDMI cables presently widespread in the market are of type A having only the number of terminals with which one channel of TMDS differential signal can be transmitted. The occupation of type A in the market may well be 100% without exaggeration. Type B HDMI connectors and HDMI cables permitting 2-channel simultaneous transmission are close to non-existent in the market and expected to be very expensive if appearing on the market.
There is also known a technique in which a compressed video signal of one channel is packetized during a blanking interval of an uncompressed video signal of another channel, and these video signals are multiplexed, to thereby achieve simultaneous transmission of two channels of video signals (see US 2006/0291569 A1).